1. Field of the Invention
The present invention relates to a motor-drive industrial robot which is suitable for being used as a painting or coating robot.
2. Prior Art
As the industrial robot used as the painting robot and the like, several kinds of playback type robots are developed and used. For example, as the painting robot which is positioned in the atmosphere where the paint solvent is volatile so that particles thereof are floating, the hydraulic robot is conventionally used because it can be designed by the explosion-proof construction with ease. However, this hydraulic robot is disadvantageous in that the maintenance thereof is troublesome. Therefore, recently, electric robot is used as the painting robot instead of the hydraulic robot.
Such electric robot is designed to repeatedly carry out the predetermined operation which is taught and programmed in advance (hereinafter, this operation is referred to as the teaching operation). This robot provides plenty of movable members such as a rotary table, a support, an arm, a wrist mechanism and the like. Each movable member is driven by its corresponding motor. Since each motor rotates at high speed, the rotation thereof is reduced by a speed reducer and then the reduced rotation is transmitted to the movable member as the predetermined torque. Since each movable member of this robot is driven by its motor as described above, it should be designed by the explosion-proof construction when it is used in the flammable atmosphere. For example, in the painting robot which may spray the flammable paint, its electric system at which the spark can occur is designed by the internal pressure explosion-proof construction.
In such internal pressure explosion-proof construction, each motor is stored in its housing. In addition, the cable to be coupled to the motor is inserted into a sealed tube to which the protective gas is supplied under the predetermined pressure. Further, this protective gas is supplied into the housing. This robot is designed such that its power supply is shut off when the protective gas in the tube leaks out so that its pressure decreases.
Since the above-mentioned conventional robot requires the speed reducer between the motor and movable member, such reducer works as the resisting force or repulsive force when the operator performs the foregoing teaching operation by holding the grip which is provided at the tip edge portion of the arm. So, the operator requires much physical power to overcome such resisting force in the teaching operation. In order to reduce necessary physical power in the teaching operation, a clutch mechanism can be provided between the reducer and movable member, by which the load of the reducer is canceled in the teaching operation. However, due to the provision of this clutch mechanism, the whole system of the robot should be complicated. Meanwhile, the conventional robot requires the maintenance of the reducer. However, since the rigidity of the reducer is relatively low, it becomes difficult to control the movable member at the tip edge portion of the arm with accuracy even if the rotation of the motor is controlled. In addition, in the robot providing with the clutch mechanism, the motor unit has heavy weight, which will reduce the operating characteristic of each movable member. This raises the cost for making the robot high. Further, it is difficult to seal the periphery of the motor shaft such that the protective gas does not leak out from the shaft, because the shaft rotates at high speed.
Meanwhile, the above-mentioned electric robot must provide a plenty of electric elements such as the motor, its wire etc., which should be constructed in the explosion-proof manner. Since the electric robot is constructed as the explosion-proof, it inevitably has several kinds of disadvantages as follows.
In case of the robot which adopts the internal pressure explosion-proof construction, the scavenge gas such as the air is blown into the space where the electric elements are arranged such that the internal pressure can be applied. By exhausting this scavenge gas to thereby scavenge the above-mentioned space, the external atmosphere is prevented from being in contact with the electric elements within the robot. However, in this conventional robot made by the internal pressure explosion-proof construction, the gas passage system thereof is complicated. Therefore, it takes much time to scavenge, because the pressure loss in such complicated gas passage system becomes large. In addition, the stagnation can be easily occurred in the gas flow, which will reduce the explosion-proof reliability. Further, in some cases, the motor bearing is exposed to the scavenge gas flow so that the lubricant thereof is blown out, which deteriorates the lubrication of the motor bearing.
Particularly, in case of the robot arm providing the wrist mechanism at its tip edge portion in which the motor for driving the wrist mechanism is equipped, the above-mentioned problems are remarkably occurred. In addition, the conventional technique cannot provide the solution by which the scavenge gas can be efficiently flown into the part where the motor is arranged.
Further, the conventional electric painting robot should arrange the wires such as the power line of the motor in the narrow and complicated space within the main unit thereof, so that the assembly operation thereof must be difficult. In addition, it is difficult to wire the robot with enough room to be remained. Due to such difficulties of wiring, excess force can be easily applied to the wires when the robot moves. Therefore, the reliability of the robot becomes low because there is a possibility in that the wires can be broken with ease.